E G Berezhko

Theoretical study of inner-shell alignment of atoms in electron impact ionisation: angular distribution and polarisation of X-rays and Auger electrons

The alignment of ions with an inner-shell vacancy resulting from ionisation by a fast charged particle is considered. The alignment has been calculated in the Born approximation using the Herman-Skillman model. The angular distribution and polarisation of characteristic X-radiation and Auger electrons from decay of aligned ions are discussed. It is shown that the theoretical anisotropy of the angular distribution is sensitive to the wavefunctions used. The results of calculations using the Herman-Skillman wavefunctions are in much better agreement with experiment than the previous calculations involving the hydrogen-like functions.

Potential-barrier effects in inner-shell photoionisation and their influence on the anisotropy of X-rays and Auger electrons

For a number of atoms, systematic calculations have been made of the alignment occurring in the photoionisation of inner subshells in the vicinity of the ionisation threshold. The influence of the centrifugal barrier in the effective partial potential on the alignment and on the anisotropy of the angular distribution and the polarisation of X-rays and Auger electrons is discussed. It is shown that the anisotropy is rather sensitive to the models used.

The theory of coincidence experiments on electron impact ionisation of inner atomic shells

A theoretical treatment is given of possible experiments on electron impact ionisation of inner atomic shells, in which an inelastically scattered electron is detected in coincidence with the decay products of the ion formed, namely with an X-ray photon or with an Auger electron. General expressions for the angular distribution and polarisation of the X-ray photons and Auger electrons are given in terms of the parameters describing the anisotropy of the ionic state, namely statistical tensors which depend on the electron scattering angle and are determined by the ionisation mechanism. The statistical tensors, the asymmetry and the polarisation of the X-rays and the asymmetry of the Auger electrons are calculated for ionisation of the 2p shell of Ar, the 3d shell of Kr and the 4d shell of Xe at different scattering angles of the fast electron.

Inner-shell alignment of atoms in ion-atom collisions. II. Electron capture

For pt.I see ibid., vol.13, p.1601 (1980). The alignment of ions with an inner-shell vacancy resulting from electron capture in ion-atom collisions is treated theoretically. The general expressions for the alignment are obtained in the Oppenheimer-Brinkman-Kramers and Born approximations. Simple analytical formulae for the alignment are derived within the framework of the hydrogenic model. The dependence of the degree of alignment on the incident particle velocity and the ratio of charges of the colliding particles is analysed. The alignment due to electron capture is shown to differ essentially from the alignment due to direct Coulomb ionisation. The sensitivity of the degree of alignment to the form of captured-electron wavefunctions and to the type of perturbing interaction is investigated. The experimental data on the angular distribution of Auger electrons in the ionisation of the 2p3/2subshell of Mg by protons and He+ ions are reanalysed taking into account the electron capture mechanism.

The effect of many-electron correlations on the alignment of ions in atomic photoionization

Abstract It is shown that the inclusion of many-electron correlations and electron shell rearrangement can significantly change the alignment of the ion arising from the photoionization of atomic subshells with j > 1 2 . The degree of alignment for photoionization of the 4d 10 subshells of Xe, Cs and Ba atoms and the 5p 6 subshell of Ba is calculated.

On the role of electron capture in the inner-shell alignment of atoms in ion-atom collisions

Abstract The alignment of the 2p 3 2 vacancy in Mg resulting from collisions with protons is calculated. Two possible mechanisms of ionisation are considered: direct Coulomb ionisation and electron capture by protons. The inclusion of electron capture leads to a marked improvement of the agreement between theory and experiment.

Excitation of resonance transitions in argon atoms by electron impact in the distorted-wave Born approximation: role of the imaginary part of the optical potential

The total and differential cross sections for the excitation of the 3p-14s1 P state in argon and also the correlation parameters lambda and chi have been calculated using the distorted-wave Born approximation. Different variants of the distorting potential are used. It is shown that the inclusion of the imaginary part of the optical potential in a semiphenomenological form allows one to improve the agreement between the calculated total and differential cross sections and experiment.

On the alignment of ions in inner-shell ionisation by heavy particle impact

The alignment of the 2p3/2 vacancy in Mg resulting from ionisation by a proton and He+ is calculated. The calculations are made in the Born approximation using the hydrogen-like and Hermann-Skillman models. The theoretical prediction is compared with experimental data.

Application of distorted-wave approximation to the study of inner-shell alignment by electron impact

The distorted-wave Born approximation is used to calculate the 2p3/2 vacancy alignment in ionisation of Mg and Ar by electron impact. The distortion of incoming and outgoing electron waves by a static atomic field is taken into account. The distorted-wave calculation allows one to explain the experimentally observed drastic increase of the alignment with decreasing incident electron energy. The threshold behaviour of the alignment in the Born approximation and in the distorted-wave approximation are discussed.

A study of the inner-shell alignment of atoms in the distorted-wave approximation

Using the distorted-wave approximation the authors have calculated the degree of alignment of the 2p3/2 subshell vacancy in Ar resulting from the ionisation of Ar atoms by electron impact. The use of the distorted-wave approximation allows one to widen the range of agreement between theory and experiment significantly.